Based on VSEPR theory, which of the following species has a trigonal pyramidal shape? Can be more than one answer. A. CO2 B. HCN C. CHCl3
The Correct Answer and Explanation is:
Correct Answer: None of the species (A. CO₂, B. HCN, C. CHCl₃) has a trigonal pyramidal shape.
Explanation:
The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the shapes of molecules based on the repulsions between electron pairs (bonding and lone pairs) around the central atom. A trigonal pyramidal molecular geometry occurs when:
- The central atom has four regions of electron density (three bonding pairs and one lone pair),
- The ideal bond angle is approximately 107°,
- The most common example is ammonia (NH₃).
Now let’s analyze the molecular shapes of the given species:
A. CO₂ (Carbon Dioxide)
- Central atom: Carbon
- Electron domains: Two double bonds (C=O on each side)
- No lone pairs on carbon
- Shape: Linear
- Bond angle: 180°
- Not trigonal pyramidal
B. HCN (Hydrogen Cyanide)
- Central atom: Carbon
- Electron domains: One single bond (C–H) and one triple bond (C≡N)
- No lone pairs on carbon
- Shape: Linear
- Bond angle: 180°
- Not trigonal pyramidal
C. CHCl₃ (Chloroform)
- Central atom: Carbon
- Electron domains: Four single bonds (one to H, three to Cl atoms)
- No lone pairs on carbon
- Shape: Tetrahedral
- Bond angle: ~109.5°
- Not trigonal pyramidal
Conclusion:
For a molecule to have a trigonal pyramidal shape, the central atom must have three bonded atoms and one lone pair. None of the given species meet this requirement. Therefore, none of them have a trigonal pyramidal geometry.
